Liquid crystal display unit and driving method therefor

ABSTRACT

A signal converting section increases a transfer rate of an input image signal to be supplied to a liquid crystal panel and, at the same time, also inserts a non-image signal for applying a predetermined voltage to liquid-crystal cells in space of the input image signal and supplies it as a picture-element signal to a source driver. To each picture cell, an input image signal and a non-image signal are sequentially written with positive or negative polarity. For all picture elements, after the input image signal is written, the non-image signal equal in polarity to the input image signal is always written. Furthermore, after the non-image signal is written, an image signal opposite in polarity to the non-image signal is always written. Thus, when an image is displayed on the liquid crystal panel in OCB mode, it is possible to prevent the occurrence of back transition and carry out image display evenly.

TECHNICAL FIELD

The present invention relates to liquid crystal devices, morespecifically, relates to a liquid crystal device using anactive-matrix-type liquid crystal panel, and can be expediently appliedto a liquid crystal device in OCB (Optically self-CompensatedBirefringence) mode.

BACKGROUND ART

A large number of liquid crystal devices have been used as a screendisplay device for a computer device, and are expected to also be usedmore in the future for TVs. However, currently widely-available liquidcrystal display devices are those in TN (Twisted Nematic) mode, having anarrow viewing angle and an insufficient response rate. This causesproblems such as reduction in contrast due to parallax and blurs inmoving pictures, posing a large problem about the display capability inTN mode for TVs.

In recent years, studies have been directed to the OCB mode instead ofthe TN mode. The OCB mode is a scheme with a wide viewing angle and ahigh-speed response compared with the TN mode. Therefore, the OCB modeis a display mode more suitable for nature motion picture display.

Hereinafter described are a liquid crystal display device and a methodof driving the same that adopt the OCB mode.

FIG. 1 illustrates the construction of a conventional liquid crystaldisplay device. In FIG. 1, the liquid crystal display device includesgate lines GL1 through GLn, source lines SL1 through SLm, a plurality ofthin-film transistors (hereinafter referred to as TFTs) 103 as switchingdevices, etc. FIG. 2 illustrates a picture element section thereof. Asillustrated in FIG. 2, a drain electrode of the TFT 103 is connected toa picture-element electrode in a picture element 104. The pictureelement 104 is structured by the picture-element electrode, a commonelectrode 201, a liquid crystal 202 held between both of theseelectrodes, and a storage capacitor 203 formed between thepicture-element electrode and the common electrode 201. The commonelectrode 201 is driven by a voltage supplied by a common drivingsection 105 illustrated in FIG. 1.

In FIG. 1, the gate driver 101 applies a voltage to the gate lines GL1through GLn for turning the TFTs 103 ON or OFF. In synchronization withdata supply to the source lines SL1 through SLm, the gate driver 101sequentially applies an ON potential to the gate lines GL1 through GLn.

The source driver 102 applies a voltage to the source lines SL1 throughSLm to supply the voltage to the respective picture elements 104. Adifference between the voltage supplied to the common electrode 201 andthe voltage supplied to each of the source lines SL1 through SLm to beapplied to the picture element 104 is a voltage between both ends of theliquid crystal 202 in the picture element 104. This voltage determinesthe transmittance of the picture element 104.

The above driving scheme is applied not only to OCB cells, but also to acase where TN-type cells are used. When the OCB cells are used, however,an activation step of starting video display requires unique driving,which is not required when the TN-type cells are used.

An OCB cell has a bend configuration enabling image display or a sprayconfiguration disabling imaged display. To cause transition from thespray configuration to the bend configuration (hereinafter referred toas transition), the unique driving is required, such as applying a highvoltage for a predetermined time. Note that the driving associated withtransition is not directly related to the present invention, andtherefore is not further described herein.

This OCB cell has a problem that, even once transition is made to thebend configuration by the above unique driving, if a voltage over apredetermined level has not been applied for over a predetermined time,the bend configuration cannot be maintained and is back to the sprayconfiguration. This phenomenon is hereinafter called “back transition”.

To suppress the occurrence of back transition, as disclosed in JapanesePatent Laid-Open Publication No. 11-109921 and Japanese Liquid CrystalSociety Journal, Apr. 25, 1999 (Vol. 3, No. 2) P.99 (17) through P.106(24), it is known that a high voltage is regularly applied to the OCBcells. Hereinafter, driving for periodically applying a high potentialin order to suppress back transition is called “anti-back transitiondriving”.

FIG. 3 illustrates potential-transmittance curves observed in generalOCB.

A curve 301 is a potential-transmittance curve at normal driving, not atanti-back transition driving, and a curve 302 is apotential-transmittance curve at anti-back transition driving. Apotential 303 indicates a critical potential Vth at which backtransition occurs at normal driving. A potential 304 is a potential whenthe transmittance is at the highest (white potential), and a potential305 is a potential when the transmittance is at the lowest (blackpotential).

At normal driving (that is, when no prevention of back transmission iscarried out), the configuration of the OCB cell is back to the sprayconfiguration when the potential becomes Vth or lower, and therefore anappropriate transmittance cannot be obtained. Thus, driving is alwaysmade with a potential not lower than Vth. In such case, however, asillustrated in FIG. 3, sufficient luminance cannot be obtained. For thisreason, the OCB requires anti-back transition driving to be carried out.

As is well known, liquid crystals typified by OCB and TN requireso-called alternating driving to be carried out. However, theabove-described Japanese Patent Laid-Open Publication No. 11-109921 andJapanese Liquid Crystal Society Journal do not disclose any specificconstruction of a liquid crystal display device in OCB mode. Therefore,both of the documents do not help specify which type of alternateinversion should be carried out. Therefore, hereinafter described is avirtual example of anti-back transition driving when the most generalalternating driving (that is, a combination of line-by-line inversionand frame-by-frame version) is carried out.

FIG. 4 is an illustration showing the construction of a liquid crystaldisplay device as the virtual example. In FIG. 4, the liquid crystaldisplay device includes a signal converting section 401, a driving pulsegenerating section 402, a source driver 403, a gate driver 404, and aliquid crystal panel 405. The signal converting section 401 doubles thespeed of an input image signal line by line, converting it into adouble-speed signal composed of a double-speed image signal and adouble-speed non-image signal. The driving pulse generating section 402generates pulses for driving the respective drivers 403 and 404. Tofacilitate understanding of the description, assume for convenience sakethat the number of source lines of the liquid crystal panel 405 is ten(SL1 through SL10), the number of gate lines is ten (GL1 through GL10),and one frame period is composed of ten horizontal periods.

Described next is an operation of anti-back transition driving to becarried out by this liquid crystal display device. An input image signalis doubled in speed line by line in the signal converting section 401,and is then supplied to the source driver 403.

FIG. 5 illustrates a specific construction of the signal convertingsection 401. Also, FIG. 6 illustrates timing of a converting operation.The control signal generating section 501 generates various controlsignals, such as a clock, from a synchronizing signal synchronized withthe input image signal. The input image signal is written in a linememory 502 in synchronization with a write clock from a control signalgenerating section 501. The image signal written in the line memory 502is read from the line memory 502 in synchronization with a read clock(having a frequency twice as much as that of the write clock) from thecontrol signal generating section 501, and this reading is carried outduring a period half of that of writing. While the image signal is beingread from the line memory 502, the output signal selecting section 504selects this image signal as an output and, during the remaining period,selects a non-image signal outputted from the non-image signalgenerating section 503 as an output. Consequently, as illustrated inFIG. 6, in one horizontal period of the input signal, the double-speednon-image signal and image signal are outputted in time sequence. Thenon-image signal is a signal for applying a predetermined high potentialto the OCB cells with predetermined periodicity.

In FIG. 4, the source driver 403 alternately inverts the output signal(double-speed signal) from the signal converting section 401 for supplyto the source lines (SL1 through SL10) of the liquid crystal panel 405.FIG. 7 is an illustration showing timing of a polarity control signaland driver driving pulses when line-by-line inversion and frame-by-frameinversion are combined as described above. The polarity control signal,which is to switch alternating polarity, is a signal obtained by XORinga frame inverting signal (A) and a line inverting signal (B), and isgenerated by the driving pulse generating section 402 illustrated inFIG. 4.

An input-output characteristic of the source driver 403 is illustratedin FIG. 8. In FIG. 8, signal outputs higher with respect to a referencepotential are illustrated as having a positive polarity, and those lowerwith respect thereto as having a negative polarity. Also, in FIG. 7,this polarity is represented as “+” or “−” in each gate-selected period.For example, “+” is indicated on a gate pulse P1 at a locationcorresponding to a period T0_1 during which the gate pulse P1 isselected. This indicates that a voltage supplied by the source driver403 during the period T0_1 has a positive polarity. As illustrated inFIG. 8, the source driver 403 supplies a positive voltage when thepolarity control signal is HI, and supplies a negative voltage when LOW.

In FIG. 7, gate pulses P1 through P10 are pulses for selecting ten gatelines (GL1 through GL10), respectively, on the liquid crystal panel 405during their HI periods. The gate pulses P1 through P10 are driven inthe following manner in accordance with timing of the double-speedsignal inputted to the source driver 403.

During the period T0_1 illustrated in FIG. 7, the gate pulse P1 becomesHI, and a positive image signal S1 is written in picture elements on thegate line GL1. During the following period T0_2, the gate pulse P7becomes HI, and a negative non-image signal is written in pictureelements on the gate line GL7. During a period T0_3, the gate pulse P2becomes HI, and a negative image signal S2 is written in pictureelements on the gate line GL2. During the following period T0_4, thegate pulse P8 becomes HI, and a positive non-image signal is written inpicture elements on the gate line GL8. Thereafter, signals aresequentially written in accordance with the polarity of the polaritycontrol signal.

In this way, each of the gate lines (GL1 through GL10) on the liquidcrystal panel 405 is selected twice during one frame period. In thepicture elements on each gate line, an image signal and a non-imagesignal are written once.

During a period T1_1 of a second frame coming next, the gate pulse P1becomes HI, and a negative image signal S′1, which is opposite inpolarity of the signal in the first frame, is written in the pictureelements on the gate line GL1. During the following period T1_2, thegate pulse P7 becomes HI, and a positive non-image signal, which isopposite in polarity of the signal in the first frame, is written on thegate line GL7. Thereafter, similarly, signals opposite in polarity tothose in the first frame are sequentially written.

As such, the image signal is made opposite in polarity to that in theprevious frame so as to avoid sticking caused on the liquid crystalpanel when signals of the same polarity are retained for a long time.

With the above-described operation , it is possible to write imagesignals as well as to periodically write non-image signals. By givingvoltages of the non-image signals as appropriate, back transition can beprevented.

In FIG. 7, however, when changes in polarity of the signals (imagesignal and non-image signal) written in each line are noted, as to thefirst line through the fifth line, after an image signal is written, anon-image signal (B) opposite in polarity to this image signal is alwayswritten. Furthermore, after the non-image signal is written, an imagesignal equal in polarity to the non-image signal is always written. Onthe other hand, as to the sixth line through the tenth line, after animage signal is written, a non-image signal equal in polarity to theimage signal is always written. Furthermore, after the non-image signalis written, an image signal opposite in polarity to the non-image signalis always written. That is, the phase relation is changed between thefirst line through fifth line and the sixth line through the tenth line.

Such change in the polarity inversion relation at a certain line willaffect charging to the liquid crystal and, consequently, become a causeof impairing evenness in image quality. Especially in recent years,liquid crystal panels have become upsized and capable of displaying withhigher definition. Accordingly, wiring resistance in a glass substratebecomes increased, and also a time allocated for recharging each pictureelement tends to be shorter. Therefore, influences caused by the changein the phase relation on recharging the picture elements are notnegligible, despite technologies for improving the capability of apicture element transistor, etc. Therefore, in the above virtualexample, a difference in luminance is disadvantageously recognizedbetween the fifth line and the sixth line.

Furthermore, compared with normal driving where non-image signals arenot inserted, the driving frequency in the above virtual example becomesdouble. Therefore, the time allocated for writing the image signal toeach picture element is shortened by half compared with normal driving.Consequently, writing of data to the picture elements may notsufficiently be carried out.

Therefore, an object of the present invention is to provide a liquidcrystal display device and a method of driving the same that cansuppress the occurrence of back transition without causing the aboveproblems when OCB cells are used and, as a result, can display a goodimage.

SUMMARY OF THE INVENTION

To achieve the above objects, the present invention has the followingaspects.

A first aspect of the present invention is directed to a liquid crystaldisplay device that displays an image by driving, based on an inputimage signal, a liquid crystal panel having a plurality of source linessupplied with a picture-element signal, a plurality of gate linessupplied with a scanning signal, and a plurality of picture-elementcells arranged in matrix on intersections of the source lines and thegate lines, including: a source driver for supplying the picture-elementsignal to the source lines; a gate driver for supplying the scanningsignal to the gate lines; driving control means for generating apolarity control signal for controlling a polarity of a voltage appliedto each of the picture-element cells, and controlling the source driverby the polarity control signal; and a signal converting section forspeeding up a transfer rate of the input image signal, and inserting anon-image signal in space of the input image signal, the non-imagesignal for applying a predetermined voltage to the liquid-crystal cells,to supply the picture-element signal to the source driver, wherein theinput image signal and the non-image signal of a positive or negativepolarity are sequentially written in each of the picture-element cells,and for all of the picture elements, after an input image signal iswritten, a non-image signal equal in polarity to the input image signalis always written, and further, after the non-image signal is written,an input image signal opposite in polarity to the non-image signal isalways written.

A second aspect of the present invention is directed to a liquid crystaldisplay device that displays an image by driving, based on an inputimage signal, a liquid crystal panel having a plurality of source linessupplied with a picture-element signal, a plurality of gate linessupplied with a scanning signal, and a plurality of picture-elementcells arranged in matrix on intersections of the source lines and thegate lines, including: a source driver for supplying the picture-elementsignal to the source lines; a gate driver for supplying the scanningsignal to the gate lines; driving control means for generating apolarity control signal for controlling a polarity of a voltage appliedto each of the picture-element cells, and controlling the source driverby the polarity control signal; and a signal converting section forspeeding up a transfer rate of the input image signal, and inserting anon-image signal in space of the input image signal, the image signalfor applying a predetermined voltage to the liquid-crystal cells, tosupply the picture-element signal to the source driver, wherein theinput image signal and the non-image signal of a positive or negativepolarity are sequentially written in each of the picture-element cells,and for all of the picture element cells, after an input image signal iswritten, a non-image signal opposite in polarity to the input imagesignal is always written, and further, after the non-image signal iswritten, an input image signal equal in polarity to the non-image signalis always written.

According to the above first and second aspects, an input image signaland a non-image signal are sequentially written in the picture-elementcells, thereby improving image quality of the moving pictures. Also, thepolarity inversion can be balanced, thereby enabling image displayevenly.

According to a third aspect of the present invention, in the first orsecond aspect, the picture-element cells are OCB cells, thepredetermined voltage to be applied to the liquid crystal is a voltagethat can prevent a back transition phenomenon of the OCB cells.

According to the above third aspect, it is possible to prevent backtransition in OCB as well as to display an image with sufficientluminance.

According to a fourth aspect of the present invention, in the first orsecond aspect, before the input image signal is written, a non-imagesignal equal in polarity to the input image signal is preliminarilywritten in the picture-element cell.

According to the above fourth aspect, writing of the input image signalbecomes easy.

According to a fifth aspect of the present invention, in the first orsecond aspect, after the non-image signal is written, a non-image signalequal in polarity to the non-image signal is further auxiliarily writtenin the picture-element cell.

According to a sixth aspect of the present invention, in the first orsecond aspect, before the non-image signal is written, an input imagesignal equal in polarity to the non-image signal is furtherpreliminarily written.

According to the above fifth and sixth aspects, writing of the non-imagesignal becomes easy.

A seventh aspect of the present invention is directed to a liquidcrystal display device that displays an image by driving, based on aninput image signal, a liquid crystal panel having a plurality of sourcelines supplied with a picture-element signal, a plurality of gate linessupplied with a scanning signal, and a plurality of picture-elementcells arranged in matrix on intersections of the source lines and thegate lines, including: a source driver for supplying the picture-elementsignal to the source lines; a gate driver for supplying the scanningsignal to the gate lines; and a signal converting section for speedingup a transfer rate of the input image signal, and inserting a non-imagesignal in space of the input image signal, the non-image signal forapplying a predetermined voltage to the liquid-crystal cells, to supplythe picture-element signal to the source driver, wherein the non-imagesignal is written simultaneously to two or more scanning linescorresponding to two or more of the gate lines.

According to the seventh aspect, an input image signal and a non-imagesignal are sequentially written in the picture-element cells, therebyimproving image quality of the moving pictures. Also, it is not requiredto convert the signal transfer rate to up to a doubled one. Therefore,writing of signals in the picture-element cells become easy.

According to an eighth aspect of the present invention, in the seventhaspect, the predetermined voltage to be applied to the liquid crystal isa voltage that can prevent a back transfer phenomenon of the OCB cells.

According to a ninth aspect of the present invention, in the seventhaspect, the liquid crystal display device further includes adjustingmeans for adjusting the input image signal so that the number ofscanning lines to be scanned for one frame period becomes N×(2M+1),where the number of the two or more scanning lines in which thenon-image signal is simultaneously written is N.

In the above ninth aspect, the number of scanning lines of the inputimage signal can be adjusted, even when not satisfying a predeterminedcondition. Therefore, irrespectively of the number of scanning lines ofthe input image signal, image display can be made more evenly.

According to a tenth aspect of the present invention, in the seventhaspect, the liquid crystal display device further includes luminancecorrecting means for correcting luminance of the input image signal at apredetermined degree so that luminance variations due to difference intime periods of retaining the non-image signal for each of thepicture-element cells are eliminated.

According to the above tenth aspect, luminance variations can beprevented by correcting the luminance.

According to an eleventh aspect of the present invention, in the seventhaspect, the liquid crystal display device further includes rearrangingmeans for rearranging a transfer order of the input image signal so thattime periods of retaining the non-image signal for each of thepicture-element cells are equal at least for two frame periods, whereinthe gate driver supplies a scanning signal corresponding to therearrangement result by the rearranging means to the gate lines.

According to the above eleventh aspect, the average insertion time ofthe non-imagine signal in each scanning line is made evenly, therebypreventing luminance variations from being perceived.

According to a twelfth aspect of the present invention, in the seventhaspect, the liquid crystal display device further includes rearrangingmeans for rearranging a transfer order of the input image signal so thata difference in time period of retaining the non-image signal becomessmall between the picture-element cells adjacent to each other, whereinthe gate driver supplies a scanning signal corresponding to therearrangement result by the rearranging means to the gate lines.

According to the above twelfth aspect, discontinuity in retaining timeof the non-image signal among the scanning lines can be resolved.Therefore, it is possible to prevent luminance variations from beingperceived.

According to a thirteenth aspect of the present invention, in theseventh aspect, the time period of retaining the non-image signal forone frame is arbitrarily adjustable by a user.

According to the above thirteenth aspect, the retaining time of thenon-image signal can be arbitrarily adjusted by the user. Therefore,image display according to user's preferences can be made.

A fourteenth aspect of the present invention is directed to a liquidcrystal display device that displays an image by driving, based on aninput image signal, a liquid crystal panel having a plurality of sourcelines supplied with a picture-element signal, a plurality of gate linessupplied with a scanning signal, and a plurality of picture-elementcells arranged in matrix on intersections of the source lines and thegate lines, including: each of the picture-element cells including: atransistor connected to the source line and the gate line; a liquidcrystal and a storage capacitor respectively connected to thetransistor; a common electrode for applying a potential to the liquidcrystal; and an other-end electrode for applying a potential to thestorage capacitor from a side opposite to a side connected to thetransistor, wherein the other-end electrode is given a potential forapplying a predetermined voltage to the liquid crystal for apredetermined time period for one frame.

According to the above fourteenth aspect, the predetermined voltage canbe applied to the liquid crystal without affecting writing of the inputimage signal. Therefore, image quality of the moving pictures can beimproved without causing problems such as image deterioration due toinsufficient recharging of the image signal or processing load on thecircuits due to speed-up of the driving frequency.

According to a fifteenth aspect of the present invention, in thefourteenth aspect, the picture-element cells are OCB cells, and thepredetermined voltage to be applied to the liquid crystal is a voltagethat can prevent a back transition phenomenon of the OCB cells.

According to a sixteenth aspect of the present invention, in thefourteenth aspect, the liquid crystal display device further includes adriver for controlling the potential to be given to the other-endelectrode.

According to the above sixteenth aspect, a desired potential can befreely applied to the other-end electrode.

According to a seventeenth aspect of the present invention, in thefourteenth aspect, the other-end electrode is connected to the gate lineof another picture-element cell adjacent to the picture-element cellincluding the other-end electrode, and the other-end electrode is giventhe potential through the gate line.

According to the above seventeenth aspect, with manipulation of thepotential given to the other gate line, it is possible to manipulate thepotential given to the other-end electrode without providing a newwiring to the liquid crystal panel, thereby preventing reduction inaperture ratio.

According to an eighteenth aspect of the present invention, in thefourteenth aspect, a range of change in a potential from the source lineto the picture-element cell is not less than one-fold and less thantwo-fold of a range of change required for changing a transmittance ofthe picture-element cell at maximum, and the other-end electrode isfurther given with a potential for changing a polarity of the voltage tobe applied to the picture-element cell.

According to the above eighteenth aspect, it is possible to reduce costof a circuit for driving the source line or cost of a driver IC.

A nineteenth aspect of the present invention is directed to a method ofdriving a liquid crystal display device that displays an image bydriving, based on an input image signal, a liquid crystal panel having aplurality of source lines supplied with a picture-element signal, aplurality of gate lines supplied with a scanning signal, and a pluralityof picture-element cells arranged in matrix on intersections of thesource lines and the gate lines, the method including: a drivercontrolling step of generating a polarity control signal for controllinga polarity of a voltage to be applied to each of the picture-elementcells, and controlling the source driver by the polarity control signal;a step of speeding up a transfer rate of the input image signal; a stepof inserting a non-image signal for applying a predetermined voltage tothe liquid-crystal cells in space of the input image signal speeded upin the transfer rate; a step of supplying the input image signal speededup in the transfer rate and having the non-image signal inserted thereinto the source line as a picture-element signal; and a step of supplyingthe scanning signal to the gate line, wherein the input image signal andthe non-image signal of a positive or negative polarity are sequentiallywritten in each of the picture-element cells, and for all of the pictureelements, after an input image signal is written, a non-image signalequal in polarity to the input image signal is always written, andfurther, after the non-image signal is written, an input image signalopposite in polarity to the non-image signal is always written.

A twentieth aspect of the present invention is directed to a method ofdriving a liquid crystal display device that displays an image bydriving, based on an input image signal, a liquid crystal panel having aplurality of source lines supplied with a picture-element signal, aplurality of gate lines supplied with a scanning signal, and a pluralityof picture-element cells arranged in matrix on intersections of thesource lines and the gate lines, the method including: a drivercontrolling step of generating a polarity control signal for controllinga polarity of a voltage to be applied to each of the picture-elementcells, and controlling the source driver by the polarity control signal;a step of speeding up a transfer rate of the input image signal; a stepof inserting a non-image signal for applying a predetermined voltage tothe liquid-crystal cells in space of the input image signal speeded upin the transfer rate; a step of supplying the input image signal speededup in the transfer rate and having the non-image signal inserted thereinto the source line as a picture-element signal; and a step of supplyingthe scanning signal to the gate line, wherein the input image signal andthe non-image signal of a positive or negative polarity are sequentiallywritten in each of the picture-element cells, and for all of the pictureelement cells, after an input image signal is written, a non-imagesignal opposite in polarity to the input image signal is always written,and further, after the non-image signal is written, an input imagesignal equal in polarity to the non-image signal is always written.

According to the above nineteenth and twentieth aspects, an input imagesignal and a non-image signal are sequentially written inpicture-element cells, thereby improving image quality of the movingpictures. Also, the polarity inversion can be balanced, thereby enablingimage display evenly.

A twenty-first aspect of the present invention is directed to a methodof driving a liquid crystal display device that displays an image bydriving, based on an input image signal, a liquid crystal panel having aplurality of source lines supplied with a picture-element signal, aplurality of gate lines supplied with a scanning signal, and a pluralityof picture-element cells arranged in matrix on intersections of thesource lines and the gate lines, the method including: a source driverfor supplying the picture-element signal to the source line; a gatedriver for supplying the scanning signal to the gate line; a step ofspeeding up a transfer rate of the input image signal; a step ofinserting a non-image signal for applying a predetermined voltage to theliquid-crystal cells in space of the input image signal; and a step ofsupplying the input image signal speeded up in transfer rate and havingthe non-image signal inserted therein to the source line as thepicture-element signal, wherein the non-image signal is simultaneouslywritten in two or more scanning lines that correspond to two or more ofthe gate lines.

According to the above twenty-first aspect, an input image signal and anon-image signal are sequentially written in the picture-element cells,thereby improving image quality of the moving pictures. Also, it is notrequired to convert the signal transfer rate to up to a doubled one.Therefore, writing of signals in the picture-element cells become easy.

A twenty-second aspect of the present invention is directed to a methodof driving a liquid crystal display device that displays an image bydriving, based on an input image signal, a liquid crystal panel having aplurality of source lines supplied with a picture-element signal, aplurality of gate lines supplied with a scanning signal, and a pluralityof picture-element cells arranged in matrix on intersections of thesource lines and the gate lines, each of the picture-element cellsincluding: a transistor connected to the source line and the gate line;a liquid crystal and a storage capacitor respectively connected to thetransistor; a common electrode for applying a potential to the liquidcrystal; and an other-end electrode for applying a potential to thestorage capacitor from a side opposite to a side connected to thetransistor, wherein the method includes a step of giving the other-endelectrode a potential for applying a predetermined voltage to the liquidcrystal for a predetermined period for one frame.

According to the above twenty-second aspect, the predetermined voltagecan be applied to the liquid crystal without affecting writing of theinput image signal. Therefore, image quality of the moving pictures canbe improved without causing problems such as image deterioration due toinsufficient recharging of the image signal or processing load on thecircuits due to speed-up of the driving frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration showing the construction of a conventionalliquid crystal display device.

FIG. 2 is an illustration showing a picture element section of theconventional liquid crystal display device.

FIG. 3 is an illustration showing a potential-transmittance curve ofgeneral OCB.

FIG. 4 is an illustration showing the construction of a liquid crystaldevice as a virtual example.

FIG. 5 is an illustration showing a specific construction of a signalconverting section 401.

FIG. 6 is an illustration showing timing of a converting operation ofthe signal converting section 401.

FIG. 7 is an illustration showing timing of an image signal and driverdriving pulses when line-by-line inversion and frame-by-frame inversionare combined.

FIG. 8 is an illustration showing an input-output characteristic of asource driver 403.

FIG. 9 is a block diagram illustrating the construction of a liquidcrystal device according to a first embodiment of the present invention.

FIG. 10 is an illustration showing timing of an input image signal, adouble-speed signal, and a polarity control signal.

FIG. 11 is an illustration showing timing of gate driver driving pulses.

FIG. 12 is a block diagram illustrating the construction of a liquidcrystal display device according to a second embodiment of the presentinvention.

FIG. 13 is an illustration showing timing of an input image signal, adouble-speed signal, and a polarity control signal.

FIG. 14 is an illustration showing timing of gate driver driving pulses.

FIG. 15 is a block diagram illustrating the construction of a liquidcrystal display device according to a third embodiment of the presentinvention.

FIG. 16 is an illustration showing timing of an input image signal, adouble-speed signal, and gate driver driving pulses.

FIG. 17 is another illustration showing timing of the input imagesignal, the double-speed signal, and the gate driver driving pulses.

FIG. 18 is a block diagram showing the construction of a liquid crystaldevice according to a fourth embodiment of the present invention.

FIG. 19 is an illustration showing timing of an input image signal, adouble-speed signal, and gate driver driving pulses.

FIG. 20 is another illustration showing timing of the input imagesignal, the double-speed signal, and the gate driver driving pulses.

FIG. 21 is a block diagram showing the construction of a liquid crystaldevice according to a fifth embodiment of the present invention.

FIG. 22 is an illustration showing a specific construction of a signalconverting section 2101.

FIG. 23 is an illustration of timing of a converting operation of thesignal converting section 2101.

FIG. 24 is an illustration of timing an input image signal, an outputsignal from the signal converting section 2101, a polarity controlsignal, and gate driver driving pulses.

FIG. 25 is a block diagram showing the construction of a liquid crystaldisplay device according to a sixth embodiment of the present invention.

FIG. 26 is an illustration showing timing of an input image signal, anoutput signal from the signal converting section 2101, a polaritycontrol signal, and gate driver driving pulses.

FIG. 27 is an illustration showing one example of driving timing whenthe total number of lines for one frame period does not satisfy apredetermined condition.

FIG. 28 is a block diagram showing the construction of a liquid crystaldisplay device according to a seventh embodiment of the presentinvention.

FIG. 29 is an illustration showing that the length of a retention timeof a non-image signal differs by line.

FIG. 30 is an illustration showing the state of luminance variations.

FIG. 31 is a block diagram illustrating a liquid crystal display deviceaccording to an eighth embodiment of the present invention.

FIG. 32 is a block diagram illustrating a liquid crystal display deviceaccording to a ninth embodiment of the present invention.

FIGS. 33A and 33B are illustrations showing timing of gate driverdriving pulses in a first frame and a second frame, respectively.

FIG. 34 is an illustration for demonstrating an other-end electrode3401.

FIG. 35 is an illustration for demonstrating an other-end driver 3501.

FIG. 36 is a block diagram illustrating the construction of a liquidcrystal device according to a tenth embodiment of the present invention.

FIG. 37 is an illustration showing a relation between a potentialsupplied to a picture element and a voltage applied to a liquid crystal202.

FIG. 38 is a block diagram illustrating the construction of a liquidcrystal device according to an eleventh embodiment of the presentinvention.

FIG. 39 is an illustration showing a relation between a potentialsupplied to the picture element and a voltage applied to the liquidcrystal 202.

FIG. 40 is a block diagram showing the construction of a liquid crystaldevice according to a twelfth embodiment of the present invention.

FIG. 41 is an illustration showing the detailed construction of a liquidcrystal panel 4005.

FIG. 42 is an illustration showing a relation between a potentialsupplied to the picture element and a voltage applied to the liquidcrystal 202.

DETAILED DESCRIPTION THE INVENTION

With reference to the drawings, various embodiments of the presentinvention are described below.

(First Embodiment)

FIG. 9 is a block diagram showing the construction of a liquid crystaldevice according to a first embodiment of the present invention. In FIG.9, the liquid crystal display device includes a signal converting unit401, a driving pulse generating section 902, a source driver 403, a gatedriver 404, and a liquid crystal panel 405. Note that the firstembodiment is different from the virtual example illustrated in FIG. 4only in the driving pulse generating section. In FIG. 9, the componentsequivalent to those illustrated in FIG. 4 are provided with the samereference numerals, and are not described herein. The driving pulsegenerating section 902 generates pulses for driving the respectivedrivers 403 and 404. To facilitate understanding of the description,assume for convenience sake that the number of source lines of theliquid crystal panel 405 is ten (SL1 to SL10), the number of gate linesis ten (GL1 to GL10), and one frame period is composed of ten horizontalperiods.

Described next is an operation of anti-back transition to be carried outby the liquid crystal device according to the first embodiment. An inputimage signal is doubled in speed line by line in the signal convertingsection 401, and is then supplied to the source driver 403.

The specific construction of the signal converting section 401 and thetiming of the converting operation have been described in thedescription of the virtual example with reference to FIG. 5 and FIG. 6,and are therefore not described herein. From the signal convertingsection 401, a non-image signal and an image signal that have beendoubled in speed line by line are outputted in time sequence during onehorizontal period of the input signal.

The source driver 403 alternately inverts the signal (double-speedsignal) outputted from the signal converting section 401 for supply tothe source lines (SL1 to SL10) of the liquid crystal panel 405.

FIG. 10 and FIG. 11 are illustrations showing, as an example ofalternate inversion, timing of a polarity control signal and timing ofeach driver driving pulse, respectively, when line-by-line inversion andframe-by-frame inversion are combined. The polarity control signal forswitching alternate polarity is generated by the driving pulsegenerating section 902 in the following manner.

As illustrated in FIG. 10, the polarity control signal is generatedbased on, an image period signal (A) indicating HI during image signalperiods (T0_1, T0_3, T0_5, . . . , T1_1, T1_3, . . . ), a frameinversion signal (B) synchronized with writing of an image signal, aframe inversion signal (C) synchronized with writing of a non-imagesignal, and a line-by-line inversion signal (D). First, a signal (E)obtained by XORing the signal (D) and the signal (B) and a signal (F)obtained by XORing the signal (D) and the signal (C) are generated.Further, such a signal (G) is generated as to become the signal (E) whenthe signal (A) is HI and become the signal (F) when the signal (A) isLOW. This signal (G) is a polarity control signal of a source signal.

Note that, in the present embodiment, the frame inversion signal (B) andthe frame inversion signal (C) have such a phase relation as that thesignal (C) trails earlier than the signal (B), as illustrated in FIG.10.

Based on the polarity control signal (G) generated in the above manner,the source driver 403 supplies a positive voltage when the polaritycontrol signal (G) is HI, and supplies a negative voltage when LOW. Theinput-output characteristic of the source driver 403 has been describedwith reference to FIG. 8. In FIG. 11, the polarity of the voltagesupplied by the source driver 403 is represented as “+” or “−” in eachgate-selected period.

In FIG. 11, gate pulses P1 through P10 are pulses for selecting ten gatelines (GL1 through GL10), respectively, on the liquid crystal panel 405during their HI periods. The gate pulses P1 through P10 are driven inthe following manner in accordance with timing of the double-speedsignal inputted to the source driver 403.

During the period T0_1 illustrated in FIG. 11, the gate pulse P1 becomesHI, and a negative image signal S1 is written in picture elements on thegate line GL1. During the following period T0_2, the gate pulse P7becomes HI, and a positive non-image signal is written in pictureelements on the gate line GL7. During the period T0_3, the gate pulse P2becomes HI, and a positive image signal S2 is written in pictureelements on the gate line GL2. During the following period T0_4, thegate pulse P8 becomes HI, a negative non-image signal is written inpicture elements on the gate line GL8. Thereafter, depending on thepolarity of the polarity control signal (G), signals are sequentiallywritten. Furthermore, during the period T0_10, the gate pulse P1 becomesHI again, and a negative non-image signal is written in the pictureelements on the gate line GL1.

In this way, each of the gate lines (GL1 through GL10) on the liquidcrystal panel 405 is selected twice during one frame period. In thepicture elements on each gate line, an image signal and a non-imagesignal are written once.

During the period T1_1 of a second frame coming next, the gate pulse P1becomes HI, and a positive image signal S′1, which is opposite inpolarity of the signal in the first frame, is written in the pictureelements on the game line GL1. During the following period T1_2, thegate pulse P7 becomes HI, and a negative non-image signal, which isopposite in polarity to the signal in the first signal, is written inthe picture elements on the gate line GL7. Thereafter, similarly,signals opposite in poiarity to those in the first frame aresequentially written.

With the above-described operation, it is possible to write imagesignals as well as to periodically write non-image signals. By givingvoltages of the non-image signals as appropriate, back transition can beprevented.

Moreover, for all picture elements, after an image signal is written, anon-image signal (B) equal in polarity to the image signal is alwayswritten. Furthermore, after the non-image signal (B) is written, theimage signal opposite in polarity to the non-image signal is alwayswritten. Therefore, the degree of writing of image signals in therespective picture elements is made even, thereby enabling image displaymore evenly.

Note that, in the present embodiment, the basic driving scheme isso-called line inversion driving, in which the polarity of the signal isinverted line by line, but the present invention is not restrictedthereto. For example, similar effects can be obtained even withso-called column inversion driving, in which signals written in pictureelements adjacent to each other on a line are opposite.

(Second Embodiment)

FIG. 12 is a block diagram illustrating the construction of a liquidcrystal display device according to a second embodiment of the presentinvention. In FIG. 12, the liquid crystal device includes a signalconverting section 401, a driving pulse generating section 1202, asource driver 403, a gate driver 404, and a liquid crystal panel 405.Note that the second embodiment is different from the first embodimentillustrated in FIG. 9 only in the driving pulse generating section. InFIG. 12, the components equivalent to those illustrated in FIG. 9 areprovided with the same reference numerals, and are not described herein.The driving pulse generating section 1202 generates pulses for drivingthe respective drivers 403 and 404. To facilitate understanding of thedescription, assume for convenient sake that the number of source linesof the liquid crystal panel 405 is ten (SL1 through SL10), the number ofgate lines is ten (GL1 through GL10), and one frame period is composedof ten horizontal periods.

Described next is an operation of anti-back transition to be carried outby the liquid crystal display device according to the second embodiment.An input image signal is doubled in speed line by line in the signalconverting section 401, and is then supplied to the source driver 403.

The specific construction of the signal converting section 401 and thetiming of the converting operation have been described in thedescription of the virtual example with reference to FIG. 5 and FIG. 6,and are therefore not described herein. From the signal convertingsection 401, a non-image signal and an image signal that have beendoubled in speed line by line are outputted in time sequence during onehorizontal period of the input signal.

The source driver 403 alternately inverts the signal (double-speedsignal) outputted from the signal converting section 401 for supply tothe source lines (SL1 through SL10) of the liquid crystal panel 405.

FIG. 13 and FIG. 14 are illustrations showing, as one example ofalternate inversion, timing of a polarity control signal and timing ofeach driver driving pulse, respectively, when line-by-line inversion andframe-by-frame inversion are combined. The polarity control signal forswitching the alternate polarity is generated by the driving pulsegenerating section 1202 in the following manner.

As illustrated in FIG. 13, the polarity control signal is generatedbased on an image period signal (A) indicating HI during image signalperiods (T0_1, T0_3, T0_5, . . . , T1_1, T1_3, . . . ), a frameinversion signal (B) synchronized with writing of an image signal, aframe inversion signal (C) synchronized with writing of a non-imagesignal, and a line-by-line inversion signal (D). First, a signal (E)obtained by XORing the signal (D) and the signal (B) and a signal (F)obtained by XORing the signal (D) and the signal (C) are generated.Further, such a signal (G) is generated as to become the signal (E) whenthe signal (A) is HI and become the signal (F) when the signal (A) isLOW. This signal (G) is a polarity control signal of a source signal.

Note that, in the present embodiment, the frame inversion signal (B) andthe frame inversion signal (C) have such a phase relation as that thesignal (C) trails earlier than the signal (B), as illustrated in FIG.13.

Based on the polarity control signal (G) generated in the above manner,the source driver 403 supplies a positive voltage when the polaritycontrol signal (G) is HI, and supplies a negative voltage when LOW. Theinput-output characteristic of the source driver 403 has been describedwith reference to FIG. 8. In FIG. 14, the polarity of the voltagesupplied by the source driver 403 is represented as “+” or “−” in eachgate-selected period.

In FIG. 14, gate pulses P1 through P10 are pulses for selecting ten gatelines (GL1 through GL10), respectively, on the liquid crystal panel 405during their HI periods. The gate pulses P1 through P10 are driven inthe following manner in accordance with timing of the double-speedsignal inputted to the source driver 403.

During the period T0_1 illustrated in FIG. 14, the gate pulse P1 becomesHI, and a negative image signal S1 is written in picture elements on thegate line GL1. During the following period T0_2, the gate pulse P7becomes HI, and a negative non-image signal is written in pictureelements on the gate line GL7. During the period T0_3, the gate pulse P2becomes HI, and a positive image signal S2 is written in pictureelements on the gate line GL2. During the following period T0_4, thegate pulse P8 becomes HI, a negative non-image signal is written inpicture elements on the gate line GL8. Thereafter, depending on thepolarity of the polarity control signal (G), signals are sequentiallywritten. Furthermore, during the period T0_10, the gate pulse P1 becomesHI again, and a positive non-image signal is written in the pictureelements on the gate line GL1.

In this way, each of the gate lines (GL1 through GL10) on the liquidcrystal panel 405 is selected twice during the one frame period. In thepicture elements on each gate line, an image signal and a non-imagesignal are written once.

During the period T1_1 of a second frame coming next, the gate pulse P1becomes HI, and a positive image signal S′1, which is opposite inpolarity of the signal in the first frame, is written in the pictureelements on the game line GL1. During the following period T1_2, thegate pulse P7 becomes HI, and a positive non-image signal, which isopposite in polarity to the signal in the first signal, is written inthe picture elements on the gate line GL7, Thereafter, similarly,signals opposite in polarity to those in the first frame aresequentially written.

With the above-described operation, it is possible to write imagesignals as well as to periodically write non-image signals. By givingvoltages of the non-image signals as appropriate, back transition can beprevented.

Moreover, for all picture elements, after an image signal is written, anon-image signal (B) opposite in polarity to the image signal is alwayswritten. Furthermore, after the non-image signal (B) is written, theimage signal equal in polarity to the non-image signal is alwayswritten. Therefore, the degree of writing of image signals in therespective picture elements is made even, thereby enabling image displaymore evenly.

Also, prior to writing of an image signal, a signal (non-image signal)equal in polarity to the image signal is always written. This makeswriting of the image signal easy.

Note that, in the present embodiment, the basic driving scheme isso-called line inversion driving, in which the polarity of the signal isinverted line by line, but the present invention is not restrictedthereto. For example, similar effects can be obtained even withso-called column inversion driving, in which signals written in pictureelements adjacent to each other on a line are opposite.

(Third Embodiment)

In the above-described first embodiment, the driving frequency is doublethat of normal driving and, as a result, the time allocated for writingan image signal in each picture element is reduced by ½. Therefore, withupsizing and high-resolution of the liquid crystal panel, writing animage signal in each picture element may not be sufficiently carriedout, in some cases.

In a third embodiment of the present invention, to solve the aboveproblem, so-called pre-charge driving is introduced to the drivingscheme of the first embodiment, where, immediately prior to writing anoriginal image signal in a picture element, a non-image signal equal inpolarity thereto is written.

FIG. 15 is a block diagram illustrating the construction of a liquidcrystal device according to the third embodiment of the presentinvention. In FIG. 15, the liquid crystal device includes a signalconverting section 401, a driving pulse generating section 1502, asource driver 403, a gate driver 404, a liquid crystal panel 405. Notethat the third embodiment is different from the first embodimentillustrated in FIG. 9 only in the driving pulse generating section. InFIG. 15, the components equivalent to those illustrated in FIG. 9 areprovided with the same reference numerals, and are not described herein.The driving pulse generating section 1502 generates pulses for drivingthe respective drivers 403 and 404. To facilitate understanding of thedescription, assume for convenience sake that the number of source linesof the liquid crystal panel 405 is ten (SL1 to SL10), the number of gatelines is eleven (GL1 to GL11), and one frame period is composed ofeleven horizontal periods.

Described next is an operation of anti-back transition to be carried outby the liquid crystal device according to the third embodiment. An inputimage signal is doubled in speed line by line in the signal convertingsection 401, and is then supplied to the source driver 403.

The specific construction of the signal converting section 401 and thetiming of the converting operation have been described in thedescription of the virtual example with reference to FIG. 5 and FIG. 6,and are therefore not described herein. From the signal convertingsection 401, a non-image signal and an image signal that have beendoubled in speed by line are outputted in time sequence during onehorizontal period of the input signal.

The source driver 403 alternately inverts the signal (double-speedsignal) outputted from the signal converting section 401 for supply tothe source lines (SL1 to SL10) of the liquid crystal panel 405.

FIG. 16 is an illustration showing, as an example of alternateinversion, timing of a polarity control signal and driver driving pulseswhen line-by-line inversion and frame-by-frame inversion a recombined.The polarity control signal for switching the alternate polarity isgenerated by the driving pulse generating section 1502 in a mannerequivalent to that in the first embodiment.

Based on the polarity control signal, the source driver 403 supplies apositive voltage when the polarity control signal is HI, and supplies anegative voltage when LOW. The input-output characteristic of the sourcedriver 403 has been described with reference to FIG. 8. In FIG. 16, thepolarity of the voltage supplied by the source driver 403 is representedas “+” or “−” each gate-selected period.

In FIG. 16, gate pulses P1 through P11 are pulses for selecting elevengate lines (GL1 through GL11), respectively, on the liquid crystal panel405 during their HI periods. The gate pulses P1 through P11 are drivenin the following manner in accordance with timing of the double-speedsignal inputted to the source driver 403.

During the period T0_1 illustrated in FIG. 16, the gate pulse P1 becomesHI, and a positive image signal S1 is written in picture elements on thegate line GL1. During the following period T0_2, the gate pulses P2 andP5 become HI, and negative non-image signals are written in pictureelements on the gate lines GL2 and GL5, respectively. During the periodT0_3, the gate pulse P2 becomes HI, and a negative image signal S2 iswritten in the picture elements on the gate line GL2. During thefollowing period T0_4, the gate pulses P3 and P6 become HI, and positivenon-image signals are written in picture elements on the gate lines GL3and GL6. Thereafter, signals are sequentially written as illustrated inFIG. 16.

In this way, each of the gate lines (GL1 through GL11) on the liquidcrystal panel 405 is selected three times during one frame period. Inthe picture elements on each gate line, one image signal and twonon-image signals are written.

During the period T1_1 of a second frame coming next, the gate pulse P1becomes HI, and a negative image signal S′1, which is opposite inpolarity of the signal in the first frame, is written in pictureelements on the game line GL1. During the following period T1_2, thegate pulses P2 and P5 become HI, and negative non-image signals, whichare opposite in polarity to those in the first signal, are written inthe picture elements on the gate lines GL2 and GL5, respectively.Thereafter, similarly, signals opposite in polarity to those in thefirst frame are sequentially written.

As described above, according to the third embodiment, prior to writingof an image signal, a non-image signal equal in polarity to the imagesignal is preliminarily written, thereby making it possible tosufficiently charge the picture elements. Therefore, the problem ofinsufficient charge caused by a short writing time can be resolved, andmore desirable display image quality can be obtained.

Note that, in the present embodiment, as illustrated in FIG. 16, thedevice is so constructed as that the non-image signal is written 7.5horizontal periods after the time when the image signal is written.Therefore, a non-image signal to be written for pre-charge prior towriting of the image signal (hereinafter referred to as pre-chargesignal) is written 0.5 horizontal period before the time when the imagesignal is written. However, as illustrated in FIG. 17, if the device isso constructed as that the non-image signal is written 6.5 horizontalperiods after the time when the image signal is written, the pre-chargesignal can be written 1.5 horizontal periods before the image signal. Assuch, the phase of the pre-charge signal is determined based on therelation in phase between the image signal and the non-image signal.

Note that, as illustrated in FIG. 16, when a period during which thepre-charge signal is selected and a period during which the image signalis selected are adjacent to each other, it is not required to insert anon-selected period between these selection periods. Therefore,influences of sluggish transmission of the gate pulses can beeliminated, which is more desirable.

Also, in the present embodiment, as illustrated in FIG. 16, it isdesirable that one frame period be an odd multiple of one horizontalperiod. Therefore, it is more desirable that a rate changing sectionusing a memory or the like be provided for changing a signal rate asappropriate so that one frame period is always an odd multiple of onehorizontal period.

Note that, in the present embodiment, the basic driving scheme isso-called line inversion driving, in which the polarity of the signal isinverted line by line, but the present invention is not restrictedthereto. For example, similar effects can be obtained even withso-called column inversion driving, in which signals written in pictureelements adjacent to each other on a line are opposite.

(Fourth Embodiment)

In the above-described second embodiment, the driving frequency isdouble that of normal driving and, as a result, the time allocated forwriting a non-image signal in each picture element is reduced to ½.Therefore, with upsizing and high-resolution of the liquid crystalpanel, writing a non-image signal in each picture element may not besufficiently carried out, in some cases.

In a fourth embodiment of the present invention, to solve the aboveproblem, so-called dual-charge driving is introduced to the drivingscheme of the second embodiment, where, immediately after writing anon-image signal in a picture element, a non-image signal equal inpolarity thereto is written.

FIG. 18 is a block diagram illustrating the construction of a liquidcrystal device according to the fourth embodiment of the presentinvention. In FIG. 18, the liquid crystal device includes a signalconverting section 401, a driving pulse generating section 1802, asource driver 403, a gate driver 404, a liquid crystal panel 405. Notethat the fourth embodiment is different from the second embodimentillustrated in FIG. 12 only in the driving pulse generating section. InFIG. 18, the components equivalent to those illustrated in FIG. 12 areprovided with the same reference numerals, and are not described herein.The driving pulse generating section 1802 generates pulses for drivingthe respective drivers 403 and 404. To facilitate understanding of thedescription, assume for convenience sake that the number of source linesof the liquid crystal panel 405 is ten (SL1 to SL10), the number of gatelines is eleven (GL1 to GL11), and one frame period is composed ofeleven horizontal periods.

Described next is an operation of anti-back transition to be carried outby the liquid crystal device according to the fourth embodiment. Aninput image signal is doubled in speed line by line in the signalconverting section 401, and is then supplied to the source driver 403.

The specific construction of the signal converting section 401 and thetiming of the converting operation have been described in thedescription of the virtual example with reference to FIG. 5 and FIG. 6,and are therefore not described herein. From the signal convertingsection 401, non-image signals and image signals that have been doubledin speed by each line are outputted in time sequence during onehorizontal period of the input signal.

The source driver 403 alternately inverts the signal (double-speedsignal) outputted from the signal converting section 401 for supply tothe source lines (SL1 to SL10) of the liquid crystal panel 405.

FIG. 19 is an illustration showing, as an example of alternateinversion, timing of a polarity control signal and driver driving pulseswhen line-by-line inversion and frame-by-frame inversion are combined.The polarity control signal for switching the alternate polarity isgenerated by the driving pulse generating section 1802 in a mannerequivalent to that in the second embodiment.

Based on the polarity control signal, the source driver 403 supplies apositive voltage when the polarity control signal is HI, and supplies anegative voltage when LOW. The input-output characteristic of the sourcedriver 403 has been described with reference to FIG. 8. In FIG. 19, thepolarity of the voltage supplied by the source driver 403 is representedas “+” or “−” in each gate-selected period.

In FIG. 19, gate pulses P1 through P11 are pulses for selecting elevengate lines (GL1 through GL11), respectively, on the liquid crystal panel405 during their HI periods. The gate pulses P1 through P11 are drivenin accordance with timing of the double-speed signal inputted to thesource driver 403 in the following manner.

During the period T0_1 illustrated in FIG. 19, the gate pulse P1 becomesHI, and a positive image signal S1 is written in picture elements on thegate line GL1. During the following period T0_2, the gate pulses P5 andP7 become HI, and positive non-image signals are written in pictureelements on the gate lines GL7 and GL5. During the period T0_3, the gatepulse P2 becomes HI, and a negative image signal S2 is written inpicture elements on the gate line GL2. During the following period T0_4,the gate pulses P6 and P8 become HI, and negative non-image signals arewritten in picture elements on the gate lines GL3 and GL6. Thereafter,signals are sequentially written as illustrated in FIG. 19.

In this way, each of the gate lines (GL1 through GL11) on the liquidcrystal panel 405 is selected three times during one frame period. Inthe picture elements on each gate, one image signal and two non-imagesignals are written.

During the period T1 ⁻ 1 of a second frame coming next, the gate pulseP1 becomes HI, and a negative image signal S′1, which is opposite inpolarity of the signal in the first frame, is written in the pictureelements on the game line GL1. During the following period T1_2, thegate pulses P5 and P7 become HI, and negative non-image signals, whichare opposite in polarity to those in the first frame, are written in thepicture elements on the gate lines GL5 and GL7, respectively.Thereafter, similarly, signals opposite in polarity to those in thefirst frame are sequentially written.

As described above, according to the fourth embodiment, after writing ofa non-image signal, another non-image signal equal in polarity to thenon-image signal is posteriorly written, thereby making it possible tosufficiently charge the picture elements. Therefore, the problem ofinsufficient charge caused by a short writing time can be improved, andmore desirable display image quality can be obtained.

Note that, in the present embodiment, as illustrated in FIG. 19,described is a case where, after writing of a non-image signal, anothernon-image signal equal in polarity to the non-image signal isposteriorly written. However, as illustrated in FIG. 20, immediatelyprior to writing of a non-image signal, an image signal equal inpolarity to the non-image signal may be used for pre-charging.

Also, in the present embodiment, as illustrated in FIG. 19, it isdesirable that one frame period be an odd multiple of one horizontalperiod. Therefore, it is more desirable that a rate changing sectionusing a memory or the like be provided for changing a signal rate asappropriate so that one frame period is always an odd multiple of onehorizontal period.

Note that, in the present embodiment, the basic driving scheme isso-called line inversion driving, in which the polarity of the signal isinverted line by line, but the present invention is not restrictedthereto. For example, similar effects can be obtained even withso-called column inversion driving, in which signals written in pictureelements adjacent to each other on a line are opposite.

(Fifth Embodiment)

FIG. 21 is a block diagram illustrating the construction of a liquidcrystal display device according to a fifth embodiment of the presentinvention. In FIG. 21, the liquid crystal device includes a signalconverting section 2101, a driving pulse generating section 2102, asource driver 403, a gate driver 404, and a liquid crystal panel 405.Note that the fifth embodiment is different from the first embodimentillustrated in FIG. 9 only in the driving pulse generating section andthe signal converting section. In FIG. 21, the components equivalent tothose illustrated in FIG. 9 are provided with the same referencenumerals, and are not described herein. The signal converting section2101 converts an input image signal in a manner that will be describedlater. The driving pulse generating section 2102 generates pulses fordriving the respective drivers 403 and 404. To facilitate understandingof the description, assume for convenience sake that the number ofsource lines of the liquid crystal panel 405 is ten (SL1 through SL10),the number of gate lines is twelve (GL1 through GL12), and one frameperiod is composed of twelve horizontal periods.

Described next is an operation of anti-back transition to be carried outby the liquid crystal display device according to the fifth embodiment.In the present embodiment, written in each picture element on the liquidcrystal panel 405 are an image signal and a non-image signalirrespective of this image signal for suppressing a back transitionphenomenon of the OCB liquid crystal, and these signals are written onceevery frame period. The signal converting section 2101 converts thedriving frequency. In the present embodiment, as one example offrequency conversion, 1.25-times frequency conversion is shown wheretransfer is made for five lines (including one line of a non-imagesignal) to the source driver 403 during four horizontal periods of theinput image signal. Hereinafter described is this 1.25-times frequencyconversion.

FIG. 22 illustrates a specific construction of the signal convertingsection 2101. FIG. 23 illustrates timing of the converting operation.The control signal generating section 2201 generates various controlsignals, such as a clock, from a synchronizing signal synchronized withthe input image signal. The input image signal is written in the linememory 502 in synchronization with a write clock from the controlgenerating section 2201. The image signal written in the line memory 502is read from the line memory 502 in synchronization with a read clock(having a frequency 1.25 times higher than that of the write clock) fromthe control signal generating section 2201, and this reading is carriedout during a period four-fifth of that of writing. While the imagesignal is being read from the line memory 502, the output signalselecting section 504 selects this image signal as an output and, duringthe remaining period, selects a non-image signal outputted from anon-image signal generating section 503 as an output. Consequently, fromthe signal converting section 2101, as illustrated in FIG. 23, anon-image signal and a image signal both made 1.25 times faster in speedare outputted in time sequence at the ratio of 1:4.

The input/output characteristic of the source driver 403 has beendescribed with reference to FIG. 8. The source driver 403 inverts thepolarity of the signal outputted from the signal converting section 2101by several lines for output.

FIG. 24 is an illustration showing timing of the signal outputted fromthe signal converting section 2101, a polarity control signal, and gatedriver driving pulses. In FIG. 24, the polarity of a voltage supplied bythe source driver 403 is represented as “+” or “−” in each gate-selectedperiod. This polarity is switched based on the polarity control signalgenerated in the driving pulse generating section 2102.

In FIG. 24, gate pulses P1 through P12 are pulses for selecting ten gatelines (GL1 through GL12), respectively, on the liquid crystal panel 405during their HI periods. The gate pulses P1 through P12 are driven inthe following manner in accordance with timing of the signal outputtedfrom the signal converting section 2101 to the source driver 403.

During a period T0_0 illustrated in FIG. 24, the gate pulses P5 throughP8 simultaneously become HI, and positive non-image signals are writtenin picture elements on the gate lines GL5 through GL8. During thefollowing periods T0_1 through T0_4, the gate pulses P1 through P4sequentially become HI, and positive image signals S1 through S4 aresequentially written on the gate line GL1 through GL4. During a periodT0_5, the gate pulses P9 through P12 simultaneously become HI, andnegative non-image signals are written on the gate lines GL9 throughGL12. During the following periods T0_6 through T0_9, the gate pulses P5through P8 sequentially become HI, and negative image signals S5 throughS8 are sequentially written on the gate lines GL5 through GL8. Here, thepicture elements on the gate lines GL5 through GL8 retain the non-imagesignal during the periods T0_0 through T0_5, the periods T0_0 throughT0_6, the periods T0_0 through T0_7, the periods T0_0 through T0_8,respectively.

In this way, each of the gate lines (GL1 through GL12) on the liquidcrystal panel 405 is selected twice during one frame period. In thepicture elements on each of the gate lines, an image signal and anon-image signal is written once.

During a period T1_0 of a second frame coming next, the gate pulses P5through P8 simultaneously become HI, and negative non-image signals,which are opposite in polarity of those in the first frame, are writtenon the gate lines GL5 through GL8. Similarly, during the followingperiods T1_1 through T1_4, the gate pulses P1 through P4 sequentiallybecome HI, and negative image signals S′1 through S′4, which areopposite in polarity of those in the first frame, are sequentiallywritten on the gate lines GL1 through GL4.

With the above-described operation-, it is possible to write imagesignals as well as to periodically write non-image signals. By givingvoltages of the non-image signals as appropriate, back transition can beprevented.

Furthermore, for all picture elements, after an image signal is written,a non-image signal opposite in polarity to the image signal is alwayswritten (that is, writing of a non-image signal becomes easy) and, stillfurther, after the non-image signal is written, an image signal oppositein polarity to the non-image signal is always written (that is, writingof an image signal becomes disadvantageous). Therefore, the degree ofwriting of image signals in the respective picture elements is madeeven, thereby enabling image display more evenly.

Also, non-image signals are simultaneously written in a plurality ofgate lines. Therefore, as illustrated in FIG. 23, a period allocated forrecharging the picture elements becomes longer than that in theabove-described virtual example and the first to fourth embodiments.Consequently, it is possible to solve the problem of insufficientrecharging caused by writing of the non-image signal, therebysuppressing image deterioration. It is also possible to prevent thetransfer rate to the source driver 403 from becoming high-speed, therebyreducing loads on circuits. Note that, as far as solving the problems ofinsufficient recharging and circuit loads is concerted, consideration isnot necessarily given to a balance in polarity changes.

Note that, in the present embodiment, the basic driving scheme isso-called line inversion driving, in which the polarity of the signal isinverted by several lines, but the present invention is not restrictedthereto. For example, similar effects can be obtained even withso-called column inversion driving, in which signals written in pictureelements adjacent to each other on a line are opposite in polarity.

Also, in the present embodiment, the driving frequency is converted by1.25 times. This is not restrictive. For example, when the number ofgate lines are n (n=2, 3, 4) and (n+1)/(n)-times conversion is carriedout, effects similar to those of the present embodiment can be obtained.

Also, in the present embodiment, the length of time from the time when anon-image signal is written on picture elements on a gate line to thetime when an image signal is written next is the one as illustrated inFIG. 24 (for example, the length of the periods T0_11 through T1_1 forthe gate line GL1). However, the present invention is not restrictedthereto. The period for inserting a non-image signal should be changedinto an optimum one as appropriate according to system changes, such asmaterial for the liquid crystal is replaced. Also, it is clear that theperiod for inserting a non-image signal will affect the brightness, andtherefore this inserting period may be arbitrarily changed by the user.

(Sixth Embodiment)

In the above-described fifth embodiment, the driving frequency is 1.25times higher than that at normal driving and, consequently, a timeallocated for writing an image signal in each picture element isshortened by 1/1.25.Therefore, with upsizing and high-resolution of theliquid crystal panel, writing an image signal in each picture elementmay not be sufficiently carried out, in some cases.

In a sixth embodiment of the present invention, to solve the aboveproblem, so-called pre-charge driving is introduced to the drivingscheme of the fifth embodiment, where, immediately prior to writing anoriginal image signal in each picture element, an image signal equal inpolarity thereto is written.

FIG. 25 is a block diagram illustrating the construction of a liquidcrystal device according to the sixth embodiment of the presentinvention. In FIG. 25, the liquid crystal device includes a signalconverting section 2101, a driving pulse generating section 2502, asource driver 403, a gate driver 404, a liquid crystal panel 405. Notethat the sixth embodiment is different from the fifth embodimentillustrated in FIG. 21 only in the driving pulse generating section. InFIG. 25, the components equivalent to those illustrated in FIG. 21 areprovided with the same reference numerals, and are not described herein.The driving pulse generating section 2502 generates pulses for drivingthe respective drivers 403 and 404.

In the present embodiment, as in the fifth embodiment, the signalconverting section 2101 converts the driving frequency. That is,transfer is made for five lines (including one line of a non-imagesignal) to the source driver 403 during four horizontal periods of theinput image signal.

The source driver 403 inverts the polarity of the signal outputted fromthe signal converting section 2101 by several lines for output.

FIG. 26 is an illustration showing timing of the input image signal, theoutput signal outputted from the signal converting section 2101, apolarity control signal, and gate driver driving pulses.

During a period T0_0 illustrated in FIG. 26, gate pulses P1 and P5through P8 simultaneously become HI, and positive non-image signals arewritten in picture elements on gate lines GL1 and GL5 through GL8.During the following period T0_1, the gate pulse P1 continues to be HIand, simultaneously, a gate pulse P2 becomes HI, and positive imagesignals S1 are written in picture elements on gate lines GL1 and GL2. Atthis time, the picture elements on the gate line GL1 have the positivenon-image signal written therein immediately before, and thereforewriting of the positive image signal S1 becomes easy. During thefollowing period T0_2, gate pulses P2 and P3 simultaneously become HI.In the picture elements on the gate line GL2 having the positive imagesignal S1 already written therein, a positive image signal S2 is alsowritten. Therefore, writing of the image signal S2 in the pictureelement on the gate line GL2 becomes easy. Similarly, during a periodT0_3, gate pulses P3 and P4 simultaneously become HI. In the pictureelements on the gate line GL3 having the positive image signal S2already written therein, a positive image signal S3 is also written.Therefore, writing of the image signal S3 in the picture elements on thegate line GL3 becomes easy. Further, during the following period T0_4,only the gate pulse P4 becomes HI. In the picture elements on the gateline GL4 having the positive image signal S3 already written therein, apositive image signal S4 is also written. Therefore, writing of theimage signal S4 in the picture elements on the gate line GL4 becomeseasy.

During the following period T0_5, gate pulses P5 and P9 through P12simultaneously become HI, and negative non-image signals are written inpicture elements on gate lines GL5 and GL9 through GL12. During thefollowing period T0_6, the gate pulse P5 continues to be HI, further agate pulse P6 simultaneously becomes HI, and negative image signals S5are written in picture elements on gate lines GL5 and GL6. At this time,the picture elements on the gate line GL5 have the negative non-imagesignal already written therein. Therefore, writing of also the negativeimage signal S5 becomes easy. Each picture element on the gate line GL5retains the non-image signal during the periods T0_0 through T0_5, andretains the image signal during the remaining period in the first frame.

During the following periods T0_7 through T0_9, image signals S6 throughS8 are sequentially written. Then, the polarity is inverted. During aperiod T0_10, the gate pulses P1 through P4 and P9 simultaneously becomeHI, and positive non-image signals are written in the picture elementson the gate lines GL1 through GL4 and GL9. At this time, each pictureelement on the gate lines GL1 through GL4 have the positive imagesignals S1 through S4 during the periods T0_1 through T0_4,respectively, and therefore writing of the non-image signal in thesepicture elements becomes easy.

Further described is a second frame. During a first period T1_0 in thesecond frame, the gate pulses P1 and P5 through P8 simultaneously becomeHI, and negative non-image signals, which are opposite in polarity tothose in the first frame, are written in the picture elements on thegate lines GL1, GL5 through GL8. During the following the period T1_1,the gate pulse P1 continues to be HI and, further the gate pulse P2becomes HI, negative image signals S′1, which are opposite in polarityto those in the first frame, are written in the picture elements on thegate lines GL1 and GL2. When the image signal S′1 is written in eachpicture element on the gate line GL1, these picture elements havealready the negative non-image signals written immediately before, andtherefore writing of the image signal S′1 becomes easy. During thefollowing period T1_2, the gate pulses P2 and P3 simultaneously becomeHI. In each picture element on the gate line GL2 having the negativeimage signal S′1 already written, also a negative image signal S′2 iswritten. Therefore, writing of the image signal S′2 in each pictureelement on the gate line GL2 becomes easy.

As described above, in the sixth embodiment, in a driving scheme forwriting an image signal twice to each picture element during one frameperiod, polarity control over the image signal and the non-image signalas illustrated in the fifth embodiment is maintained, and furtherpre-charging to each picture element is carried out. Thus, it ispossible to solve the problem of insufficient writing of the imagesignal.

Note that, in the present embodiment, the basic driving scheme isso-called line inversion driving, in which the polarity of the signal isinverted line by line, but the present invention is not restrictedthereto. For example, similar effects can be obtained even withso-called column inversion driving, in which signals written in pictureelements adjacent to each other on a line are opposite.

Also, in the present embodiment, the driving frequency is converted by1.25 times. This is not restrictive. For example, when the number ofgate lines are n (n=2, 3, 4) and (n+1)/(n)-times conversion is carriedout, effects similar to those of the present embodiment can be obtained.

Note that, in the present embodiment, pre-charging is applied to thedriving scheme for carrying out (n+1)/(n)-times speed conversion.Dual-charge driving as shown in the fourth embodiment can be applied tothe scheme for carrying out (n+1)/(n)-times speed conversion.Especially, the polarity of non-image signals simultaneously written ona plurality of gate lines are opposed to the polarity of the imagesignals previously written, writing of the non-image signals becomedisadvantageous. However, after writing the non-image signals, othernon-image signals equal in polarity to the non-image signals (that is,opposite in polarity to the image signals written prior to thesenon-image signals) are auxiliarily written again (dual-charge), therebyreliably writing the non-image signals. As evident from the foregoing,timing of writing again non-image signals equal in polarity of thealready-written non-image signals is, for example, after ten scanningperiods in a case of the driving scheme for carrying out 1.25-timesspeed conversion (relative positional relation such as the period T0_10with respect to the period T0_0).

(Seventh Embodiment)

In the driving scheme shown in the above-described fifth and sixthembodiments, to prevent loss of image quality, the number of linesduring one frame period is subjected to restrictions. Specifically, inthe driving scheme shown in the fifth embodiment, when the number ofgate lines on which non-image signals are simultaneously written is N,the total number of lines Y during one frame period should be N×(2M+1)(M is an integer not less than 1). Shown in the fifth embodiment and thesixth embodiment are examples where N=4 and Y=12.

FIG. 27 is an illustration showing driving timing where N=4 and Y=13 inthe driving scheme shown in the sixth embodiment, as one example of acase where the total number of lines Y during one frame period does notsatisfy the above condition.

As illustrated in FIG. 27, periods during which picture elements on gatelines GL1 through GL4 retain an image signal are periods T0_1 throughT0_9, periods T0_2 through T0_9, periods T0_3 through T0_9, and periodsT0_4 through T0_9, respectively. On the other hand, periods during whicheach picture element on a gate line GL5 retains an image signal areperiods T0_6 through T0_14. That is, the periods during which eachpicture element on the gate line GL5 retains the image signal becomeequal in length to the periods during which each picture element on thegate line GL1 retains the image signal. Similarly, the periods duringwhich each picture element on the gate lines GL6 through GL8 retains theimage signal become equal in length to the periods during which eachpicture element on the gate lines GL2 through GL4 retains the imagesignal.

On the other hand, periods during which each picture element on the gatelines GL9 through GL12 retains the image signal are periods T0_11through T1_4, periods T0_12 through T1_4, periods T0_13 through T1_4,and periods T0_14 through T1_4, respectively, and each include a periodT0_16. Therefore, those periods differ in length from the periods duringwhich each picture element on the other gate lines retains the imagesignal. As a result, a difference in brightness occurs between a displayportion corresponding to the gate lines GL1 through GL8 and a displayportion corresponding to the gate lines GL9 through GL12.

Therefore, in a seventh embodiment of the present invention, a means foradjusting the number of gate lines to be scanned for one frame period isnewly provided, thereby adjusting the total number of scanning lines Yfor one frame period of the input image signal to N×(2M+1), when Y isnot N×(2M+1).

FIG. 28 is a block diagram illustrating a liquid crystal display deviceaccording to a seventh embodiment of the present invention. In FIG. 28,the liquid crystal display device includes a signal converting section2101, a drive pulse generating section 2802, a source driver 403, a gatedriver 404, a liquid crystal panel 405, a number-of-lines adjustingsection 2806, and a frame memory 2807. Note that the seventh embodimentis different from the sixth embodiment illustrated in FIG. 25 only inthat the number-of-lines adjusting section 2806 and the frame memory2807 are newly provided. In FIG. 28, the components equivalent to thoseillustrated in FIG. 25 are provided with the same reference numerals,and are not described herein.

Described below is a driving scheme of the liquid crystal display deviceaccording to the seventh embodiment. In synchronization with referencetiming of a predetermined image signal, writing and reading of the imagesignal to and from the frame memory 2807 is carried out. At this time,the frequency of a clock used for reading the image signal from theframe memory 2807 is made lower than the frequency of a clock used forwriting the image signal in the frame memory 2807. Here, with the numberof image signals during one horizontal period maintained, the horizontalperiod becomes longer, and also with one frame period maintained, thenumber of lines during one frame period can be reduced. Thus, when thenumber of lines Y during one frame period of the input image signal isnot N×(2M+1), this number can be adjusted to N×(2M+1). Consequently,dispersion of the periods for retaining the image signal can besuppressed, thereby enabling high-quality display.

Note that, in the present embodiment, the number-of-lines convertingsection 2806 carries out conversion so that the number of lines isreduced from Y to Y′ (≦Y). This is because, in general, an image signalincludes a blanking period not related to an image to be displayed and,even if the total number of lines during one frame period is reduced,any part of video to be displayed will not be dropped. Furthermore, itis more advantageous to reduce the number of lines than to increase thenumber of lines because the operation frequency is reduced. However,when the total number of lines Y is not more than the number of lines ofthe image signals to be displayed, such adjustment as to satisfy Y′>Ymay be carried out. This adjustment is made possible by making thefrequency of the clock used for reading the image signal from the framememory 2807 higher than the frequency of the clock used for writing theimage signal in the frame memory 2807.

Note that, in the present embodiment, a driving with pre-charging hasbeen described as an example. However, pre-charge driving is notnecessarily carried out together.

(Eighth Embodiment)

In the above-described fifth embodiment, as illustrated in FIG. 24, thelength of the periods for retaining the non-image signal during oneframe period is varied by line. As illustrated in FIG. 29, the largerthe number of lines on which the non-image signals are simultaneouslywritten, the larger the variation. Consequently, luminance variationscan be disadvantageously perceived on a display screen. In an example ofFIG. 29, luminance variations by a unit of six lines as illustrated inFIG. 30 can be disadvantageously perceived. In an eighth embodiment,these luminance variations are resolved by correcting the luminance ofthe input image signal.

FIG. 31 is a block diagram illustrating the construction of a liquidcrystal display device according to the eighth embodiment. In FIG. 31,the liquid crystal display device includes a luminance correctingsection 3108, a signal converting section 3101, a driving pulsegenerating section 3102, a source driver 403, a gate driver 404, and aliquid crystal panel 405. The signal converting section 3101 includes aline memory 502. In FIG. 31, the components equivalent to thoseillustrated in FIG. 21 or FIG. 22 are provided with the same referencenumerals, and are not described herein.

The signal converting section 3101 and the driving pulse generatingsection 3102 respectively carry out predetermined signal processing soas to achieve a driving scheme illustrated in FIG. 29. This signalprocessing is evident from the above description of the embodiments, andtherefore not described herein. The luminance correcting section 3108corrects the luminance of the input image signal at a predetermineddegree previously obtained through an experiment, etc., so thatluminance variations as illustrated in FIG. 30 are eliminated. As to ascheme for correction, various schemes can be used, such as a schemeusing a table, or a scheme for using a multiplier.

As such, by correcting the luminance of the input image signal line byline, it is possible to prevent the occurrence of luminance variationsdue to variations in time for inserting a non-image signal among thelines.

(Ninth Embodiment)

FIG. 32 is a block diagram illustrating the construction of a liquidcrystal display device according to a ninth embodiment of the presentinvention. In FIG. 32, the liquid crystal display device includes asignal converting section 3201, a driving pulse generating section 3202,a source driver 403, a gate driver 404, and a liquid crystal panel 405.The signal converting section 3201 includes a memory 3209. In FIG. 32,the components equivalent to those illustrated in FIG. 21 are providedwith the same reference numerals, and are not described herein.

The signal converting section 3201 converts the input image signal sothat the driving frequency is multiplied by 7/6 and, at the same time,rearranges the writing order by line. For these conversion andrearrangement, the memory 3209 is used.

In the above-described eighth embodiment, luminance variations aresolved by correcting the image signal. In the present invention, on theother hand, luminance variations are solved by rearranging the scanningorder by frame. Hereinafter, with reference to FIG. 33A and FIG. 33B,driving is described.

FIG. 33A is an illustration showing timing of each of gate driverdriving pulses in a first frame. FIG. 33B is, on the other hand, anillustration showing timing of each of gate driver driving pulses in asecond frame. In the first frame, as illustrated in FIG. 33A, scanningis carried out in a direction from a gate line GL6 to a gate line GL1,and then in a direction from a gate line GL7 to a gate line GL12. In thefollowing second frame, as illustrated in FIG. 33B, scanning is carriedout in a direction from the gate line GL1 to the gate line GL6, and thenin a direction from the gate line GL12 to the gate line GL7. Thereafter,scanning illustrated in FIG. 33A and scanning illustrated in FIG. 33Bare alternately carried out by one frame.

As a result of such driving, all lines become equal in the averagelength of periods for every two frames, the periods during which thenon-image signal is inserted. Furthermore, as exemplarily illustrated inFIG. 29, discontinuity in the periods of retaining the non-image signalbetween the gate lines GL6 and GL7 can be resolved. Therefore, noluminance variations can be perceived.

Note that, for carrying out such scanning, the signal converting section3201 rearranges the image signals and converts the driving frequency.The construction for carrying out such signal processing has been knownto the public, and therefore is not described herein.

As described above, according to the ninth embodiment, the averageperiods during which the non-image signal is inserted can be equalizedin each gate by changing the scanning direction for each frame.Therefore, it is possible to prevent luminance variations from beingperceived.

(Tenth Embodiment)

In the above-described first to ninth embodiments, a predeterminedvoltage for preventing back transition is applied as a non-image signalto a liquid crystal through a source line. In the following embodiments,on the other hand, a predetermined voltage is applied to the liquidcrystal by controlling the potential at the electrode 3401 of a pictureelement section illustrated in FIG. 34. As illustrated in FIG. 34, thepicture element section of the liquid crystal panel has, in general, aliquid crystal 202 held between a picture element electrode and a commonelectrode 201, and a storage capacitor 203 formed between the pictureelement electrode and the electrode 3401. Note that, in FIG. 34, thecomponents equivalent in structure to those in FIG. 2 are provided withthe same reference numerals, and are not described herein. In general,the electrode 3401 is connected to the common electrode 201 asillustrated in FIG. 2. In the following embodiments, however, theelectrode 3401 is an independent electrode from the common electrode201. In the following description, for convenience sake, the electrode3401 is referred to as “the other-end electrode”. That is, of theelectrodes of the storage capacitor 203 at both ends, the one located ona side that is not connected to a drain line is called “the other-endelectrode”.

Hereinafter described is a liquid crystal display device according to atenth embodiment of the present invention. In the tenth embodiment, tomanipulate the electrode of the above-described other-end electrode3401, an other-end driver 3501 is provided as illustrated in FIG. 35.FIG. 36 is a block diagram illustrating the construction of the liquidcrystal display device according to the tenth embodiment. In FIG. 36,the liquid crystal display device includes a signal processing section3601, a driving pulse generating section 3602, a gate driver 101, asource driver 102, a liquid crystal panel 3605, and the other-end driver3501. Note that, in FIG. 35 and FIG. 36, the components equivalent instructure to those in FIG. 1 or FIG. 2 are provided with the samereference numerals, and are not described herein.

The signal processing section 3601 carries out normal signal processingassociated with image processing, and is the same as a conventional one.The driving pulse generating section 3602 generates a control signal tobe supplied to each driver, and is the same as a conventional one,except for generating a control signal for the other-end driver. Thatis, processing in the gate driver 101 and the source driver 102 issimilar to the conventional one. The liquid crystal display device ofthe tenth embodiment is different from the conventional one in that apotential for preventing back transition is applied to the liquidcrystal panel 3605 through the other-end driver 3501. Hereinafterdescribed is the operation of the present embodiment with reference toFIG. 37.

A potential Vg of each of gate lines (GL1, GL2, . . . ) sequentiallybecomes ON for each frame in synchronization with a data potential Vssupplied to a source line (SL1, SL2, . . . ). In an example illustratedin FIG. 37, the polarity of the voltage supplied to the source line isswitched by each source line and each frame. In the normal liquidcrystal panel as illustrated in FIG. 2, a difference between thepotential given to the picture element electrode through the source linein the above described manner and the potential of the common electrode201 is a voltage to be applied to the liquid crystal 202 in the pictureelement 104. The voltage applied to the liquid crystal 202 determines atransmittance of this picture element 104.

In the present embodiment, on the other hand, the potential of theother-end electrode 3401 influences the voltage applied to the liquidcrystal 202 through the storage capacitor 203. Therefore, as exemplarilyillustrated in FIG. 37, by changing a potential Ve of the other-endelectrode 3401, the potential difference between both ends of the liquidcrystal 202 can be manipulated.

When a potential is given to the other-end electrode 3401, the amount ofchange in voltage applied to the liquid crystal 202 (cumulativepotential) Vp is represented as the following equation (1), where thestorage capacitor is Cst, a liquid crystal capacitance is Clc, aparasitic capacitance between the gate and the drain not shown is Cgd,and a voltage change in Ve is Ve+ or Ve−.Vp=Cst/(Clc+Cst+Cgd)×(Ve+ or Ve−)  (1)

As shown in the above equation, by manipulating Ve+ and Ve− asappropriate, a voltage required for preventing back transition can beapplied to the liquid crystal 202 as appropriate. That is,irrespectively of the potential given to the liquid crystal through thesource line, effective voltages can be arbitrarily (the above-describedVp) accumulated. Therefore, without shortening the time for writing theimage signal, the predetermined voltage for preventing back transitioncan be regularly (for example, 20% of one frame period for each frame)applied to the liquid crystal 202.

As described above, according to the tenth embodiment, the predeterminedvoltage can be applied to the liquid crystal 202 without influencingwriting of the image signal. This does not pose such problems as imagedeterioration due to insufficient recharge of the image signal or loadincrease on circuits due to high speed of the driving frequency.

(Eleventh Embodiment)

In the above-described tenth embodiment, alternate inversion of thevoltage to be applied to the liquid crystal 202 is achieved by invertingthe polarity of the source-line potential. For carrying out suchdriving, however, the source line has to be supplied with a potential atleast double in width of the potential (black potential) 305 when thetransmittance is at the lowest as illustrated in FIG. 3. In the presentembodiment, on the other hand, alternate inversion driving and anti-backtransition preventing driving are simultaneously achieved while thesource line is supplied with a potential one-fold in width of thepotential 305 (hereinafter referred to as one-fold potential)illustrated in FIG. 3.

FIG. 38 is a block diagram illustrating a liquid crystal display deviceaccording to an eleventh aspect of the present invention. In FIG. 38,the liquid crystal display device includes a signal processing section3801, a driving pulse generating section 3802, a gate driver 101, asource driver 102, the other-end driver 3501, and a liquid crystal panel3605. Note that, in FIG. 38, the components equivalent in structure tothose in FIG. 36 are provided with the same reference numerals, and arenot described herein.

Described first is a mechanism for achieving alternate inversion drivingwhile supplying a one-fold potential to the source line.

As illustrated in FIG. 39, while agate is ON, a potential Ve of theother-end electrode 3401 is temporarily increased (Vge+) or lowered(Vg−), and then is returned to the original potential after the gate isOFF, thereby manipulating the voltage to be applied to the liquidcrystal through a storage capacitor. An amount of change in voltage tobe applied to the liquid crystal Vcc is represented by the followingequation (2) where a change in voltage of Ve is Vge+ or Vge−.Vcc=Cst/(Clc+Cst+Cgd)×(Vge+ or Vge−)  (2)

Note that, of the image signals supplied through the source lines, partto be written as negative in the end is subjected to processing, such asbit inversion, by the signal processing section 3801, for example, sothat the luminance when the signal is written as negative coincides withthe original luminance.

With such driving as described above, alternate inversion driving can becarried out while a one-fold potential is supplied to the source line.

On the other hand, as illustrated in FIG. 39, after a source-linepotential is written in the liquid crystal 202, the potential in theother-end electrode 3401 is further changed after 80% of the period ofone frame has passed, for example, and then the potential of theother-end electrode 3401 is further changed (Ve+ or Ve−) and kept inthat state. With this, the voltage required for preventing backtransition can be applied to the liquid crystal 202 through the storagecapacitor 203.

The amount of change Vp in potential applied to the liquid crystal canbe represented as the above equation (1), where the amount of change inVe is Ve+ or Ve−.

As described above, according to the eleventh embodiment, in addition tothe effects of the tenth embodiment, it is possible to carry outalternate inversion driving while driving the source line by a one-foldpotential. Therefore, it is possible to reduce cost of a circuit fordriving the source line or cost of a driver IC.

(Twelfth Embodiment)

In the above tenth and eleventh embodiments, the other-end electrode3401 is driven by the other-end driver 3401. However, such driving hassome disadvantages, such as requiring a new driver, or providing a newwiring to the liquid crystal panel 3605, resulting in reduction inaperture ratio. In the present embodiment, the other-end electrode 3401is connected to a gate line of an adjacent picture element (hereinafterreferred to as preceding-step gate) for supplying a potential to theother-end electrode 3401 for preventing back transition, therebypreventing the above disadvantages.

FIG. 40 is a block diagram illustrating the construction of a liquidcrystal display device according to a twelfth embodiment of the presentinvention. In FIG. 40, the liquid crystal display device includes asignal processing section 3601, a driving pulse generating section 4002,a gate driver 101, a source driver 102, and a liquid crystal panel 4005.Note that, in FIG. 40, the components equivalent to those in FIG. 36 areprovided with the same reference numerals, and are not described herein.

FIG. 41 illustrates the detailed construction of the liquid crystalpanel 4005. In FIG. 41, the other-end electrode 3401 is connected to apreceding-step gate 4102, which is an adjacent gate line.

In the present embodiment, as illustrated in FIG. 42, after a sourceline potential is written in the liquid crystal 202 and then after 80%,for example, of the period of one frame passes, the potential of thepreceding-step gate Vg(n−1) is changed (Ve+ or Ve−) and kept in thatstate. With this, the voltage required for preventing back transitioncan be applied to the liquid crystal 202 through the storage capacitor203.

As described above, according to the twelfth embodiment, the other-endelectrode 3401 is connected to the preceding-step gate, and thepotential given to this preceding-step gate is manipulated forpreventing a back transition phenomenon. Also, the liquid crystal panel3605 does not have to be provided with a new wiring, and therefore theproblem of reduction in aperture ratio does not occur. Also, no newdriver is required.

The various embodiments of the present invention have been describedabove. Note that, as the driving scheme of these embodiments, it isgenerally known that periodically applying a high voltage (voltage atblack level) to the liquid crystal is effective to improve displayquality of moving pictures. Therefore, even if the liquid-crystal cellsare not OCB cells, it is effective to apply the driving scheme of thepresent invention as a driving scheme suitable for moving pictures.

INDUSTRIAL APPLICABILITY

As described above, the liquid crystal display device according to thepresent invention achieves improvements in evenness in image display orsolves insufficiency in recharge at the time of periodically writing anon-image signal in addition to an image signal, thereby enabling imagedisplay with higher image quality.

1. A liquid crystal display device for displaying an image by driving,based on an input image signal, a liquid crystal panel having aplurality of source lines supplied with a picture-element signal, aplurality of gate lines supplied with a scanning signal, and a pluralityof picture-element cells arranged in a matrix on intersections of thesource lines and the gate lines, the liquid crystal display devicecomprising: a source driver for supplying the picture-element signal tothe source lines; a gate driver for supplying the scanning signal to thegate lines; driving control means for generating a polarity controlsignal for controlling a polarity of a voltage applied to each of thepicture-element cells, and controlling the source driver by the polaritycontrol signal; and a signal converting section for speeding up atransfer rate of the input image signal, and inserting a non-imagesignal in space of the input image signal, the non-image signal forapplying a predetermined voltage to the picture-element cells, to supplythe picture-element signal to the source driver, wherein the input imagesignal and the non-image signal of a positive polarity or a negativepolarity are sequentially written in each of the picture-element cells,and for all of the picture element cells, after an input image signal iswritten, a non-image signal equal in polarity to the input image signalis always written, and further, after the non-image signal is written,an input image signal opposite in polarity to the non-image signal isalways written.
 2. The liquid crystal display device according to claim1, wherein the picture-element cells are OCB cells, and thepredetermined voltage to be applied to the picture-element cells is avoltage that can prevent a back transition phenomenon of the OCB cells.3. The liquid crystal display device according to claim 1, whereinbefore the input image signal is written, a non-image signal equal inpolarity to the input image signal is preliminarily written in thepicture-element cells.
 4. The liquid crystal display device according toclaim 1, wherein after the non-image signal is written, a non-imagesignal equal in polarity to the non-image signal is further auxiliarilywritten in the picture-element cells.
 5. The liquid crystal displaydevice according to claim 1, wherein before the non-image signal iswritten, an input image signal equal in polarity to the non-image signalis further preliminarily written in the picture-element cells.
 6. Aliquid crystal display device for displaying an image by driving, basedon an input image signal, a liquid crystal panel having a plurality ofsource lines supplied with a picture-element signal, a plurality of gatelines supplied with a scanning signal, and a plurality ofpicture-element cells arranged in a matrix on intersections of thesource lines and the gate lines, the liquid crystal display devicecomprising: a source driver for supplying the picture-element signal tothe source lines; a gate driver for supplying the scanning signal to thegate lines; driving control means for generating a polarity controlsignal for controlling a polarity of a voltage applied to each of thepicture-element cells, and controlling the source driver by the polaritycontrol signal; and a signal converting section for speeding up atransfer rate of the input image signal, and inserting a non-imagesignal in space of the input image signal, the non-image signal forapplying a predetermined voltage to the picture-element cells, to supplythe picture-element signal to the source driver, wherein the input imagesignal and the non-image signal of a positive polarity or a negativepolarity are sequentially written in each of the picture-element cells,and for all of the picture element cells, after an input image signal iswritten, a non-image signal opposite in polarity to the input imagesignal is always written, and further, after the non-image signal iswritten, an input image signal equal in polarity to the non-image signalis always written.
 7. The liquid crystal display device according toclaim 6, wherein the picture-element cells are OCB cells, and thepredetermined voltage to be applied to the picture-element cells is avoltage that can prevent a back transition phenomenon of the OCB cells.8. The liquid crystal display device according to claim 6, whereinbefore the input image signal is written, a non-image signal equal inpolarity to the input image signal is preliminarily written in thepicture-element cells.
 9. The liquid crystal display device according toclaim 6, wherein after the non-image signal is written, a non-imagesignal equal in polarity to the non-image signal is further auxiliarilywritten in the picture-element cells.
 10. The liquid crystal displaydevice according to claim 6, wherein before the non-image signal iswritten, an input image signal equal in polarity to the non-image signalis further preliminarily written in the picture-element cells.
 11. Aliquid crystal display device for displaying an image by driving, basedon an input image signal, a liquid crystal panel having a plurality ofsource lines supplied with a picture-element signal, a plurality of gatelines supplied with a scanning signal, and a plurality ofpicture-element cells arranged in a matrix on intersections of thesource lines and the gate lines, the liquid crystal display devicecomprising: a source driver for supplying the picture-element signal tothe source lines; a gate driver for supplying the scanning signal to thegate lines; a signal converting section for speeding up a transfer rateof the input image signal, and inserting a non-image signal in space ofthe input image signal, the non-image signal for applying apredetermined voltage to the picture-element cells, to supply thepicture-element signal to the source driver; and adjusting means foradjusting the input image signal so that a number of scanning lines tobe scanned for one frame period becomes N×(2M+1), where N is a number oftwo or more scanning lines in which the non-image signal issimultaneously written and M is an integer not less than 1, wherein thenon-image signal is written simultaneously to the two or more scanninglines corresponding to two or more of the gate lines.
 12. A liquidcrystal display device for displaying an image by driving, based on aninput image signal, a liquid crystal panel having a plurality of sourcelines supplied with a picture-element signal, a plurality of gate linessupplied with a scanning signal, and a plurality of picture-elementcells arranged in a matrix on intersections of the source lines and thegate lines, the liquid crystal display device comprising: a sourcedriver for supplying the picture-element signal to the source lines; agate driver for supplying the scanning signal to the gate lines; asignal converting section for speeding up a transfer rate of the inputimage signal, and inserting a non-image signal in space of the inputimage signal, the non-image signal for applying a predetermined voltageto the picture-element cells, to supply the picture-element signal tothe source driver; and luminance correcting means for correctingluminance of the input image signal at a predetermined degree so thatluminance variations due to a difference in time periods of retainingthe non-image signal for each of the picture-element cells areeliminated, wherein the non-image signal is written simultaneously totwo or more scanning lines corresponding to two or more of the gatelines.
 13. A liquid crystal display device for displaying an image bydriving, based on an input image signal, a liquid crystal panel having aplurality of source lines supplied with a picture-element signal, aplurality of gate lines supplied with a scanning signal, and a pluralityof picture-element cells arranged in a matrix on intersections of thesource lines and the gate lines, the liquid crystal display devicecomprising: a source driver for supplying the picture-element signal tothe source lines; a gate driver for supplying the scanning signal to thegate lines; a signal converting section for speeding up a transfer rateof the input image signal, and inserting a non-image signal in space ofthe input image signal, the non-image signal for applying apredetermined voltage to the picture-element cells, to supply thepicture-element signal to the source driver; and rearranging means forrearranging a transfer order of the input image signal so that timeperiods of retaining the non-image signal for each of thepicture-element cells are equal at least for two frame periods, whereinthe non-image signal is written simultaneously to two or more scanninglines corresponding to two or more of the gate lines, and the gatedriver supplies the scanning signal corresponding to a rearrangementresult by the rearranging means to the gate lines.
 14. A liquid displaydevice for displaying an image by driving, based on an input imagesignal, a liquid crystal panel having a plurality of source linessupplied with a picture-element signal, a plurality of gate linessupplied with a scanning signal, and a plurality of picture-elementcells arranged in a matrix on intersections of the source lines and thegate lines, the liquid crystal display device comprising: a sourcedriver for supplying the picture-element signal to the source lines; agate driver for supplying the scanning signal to the gate lines; asignal converting section for speeding up a transfer rate of the inputimage signal, and inserting a non-image signal in space of the inputimage signal, the non-image signal for applying a predetermined voltageto the picture-element cells, to supply the picture-element signal tothe source driver; and rearranging means for rearranging a transferorder of the input image signal so that a difference in time period ofretaining the non-image signal becomes small between the picture-elementcells adjacent to each other, wherein the non-image signal is writtensimultaneously to two or more scanning lines corresponding to two ormore of the gate lines, and the gate driver supplies the scanning signalcorresponding to a rearrangement result by the rearranging means to thegate lines.
 15. A method of driving a liquid crystal display device thatdisplays an image by driving, based on an input image signal, a liquidcrystal panel having a plurality of source lines supplied with apicture-element signal, a plurality of gate lines supplied with ascanning signal, and a plurality of picture-element cells arranged in amatrix on intersections of the source lines and the gate lines, themethod comprising: generating a polarity control signal for controllinga polarity of a voltage to be applied to each of the picture-elementcells; speeding up a transfer rate of the input image signal; insertinga non-image signal for applying a predetermined voltage to thepicture-element cells in space of the input image signal speeded up inthe transfer rate; supplying the input image signal speeded up in thetransfer rate and having the non-image signal inserted therein to thelines as the picture-element signal, based on the polarity controlsignal; and supplying the scanning signal to the gate lines, wherein theinput image signal and the non-image signal of a positive polarity or anegative polarity are sequentially written in each of thepicture-element cells, and for all of the picture-element cells, afteran input image signal is written, a non-image signal equal in polarityto the input image signal is always written, and further, after thenon-image signal is written, an input image signal opposite in polarityto the non-image signal is always written.
 16. A method of driving aliquid crystal display device that displays an image by driving, basedon an input image signal, a liquid crystal panel having a plurality ofsource lines supplied with a picture-element signal, a plurality of gatelines supplied with a scanning signal, and a plurality ofpicture-element cells arranged in a matrix on intersections of thesource lines and the gate lines, the method comprising: generating apolarity control signal for controlling a polarity of a voltage to beapplied to each of the picture-element cells; speeding up a transferrate of the input image signal; inserting a non-image signal forapplying a predetermined voltage to the picture-element cells in spaceof the input image signal speeded up in the transfer rate; supplying theinput image signal speeded up in the transfer rate and having thenon-image signal inserted therein to the source lines as thepicture-element signal, based on the polarity control signal; andsupplying the scanning signal to the gate lines, wherein the input imagesignal and the non-image signal of a positive polarity or a negativepolarity are sequentially written in each of the picture-element cells,and for all of the picture element cells, after an input image signal iswritten, a non-image signal opposite in polarity to the input imagesignal is always written, and further, after the non-image signal iswritten, an input image signal equal in polarity to the non-image signalis always written.
 17. A liquid crystal display device for displaying animage on a liquid crystal panel based on an input image signal, theliquid crystal panel having a plurality of source lines supplied with aimage-signal and non-image signal, a plurality of gate lines suppliedwith a scanning signal, and a plurality of picture-element cellsarranged in a matrix on intersections of the source lines and the gatelines, the liquid crystal display device comprising: a source driver forsupplying the image-signal and the non-image signal to the soure lines;a gate driver for supplying the scanning signal to the gate lines; adriving controller for controlling a polarity of the source driver; asignal converter for speeding up a transfer rate of the input imagesignal, and inserting a non-signal in space of the input image signal,the non-image signal for applying a predetermined voltage to thepicture-element cells; wherein a polarity of the image signal and thenon-image signal turn over in one frame period; the image signal whichis sequentially written after a non-image signal on the source line hasboth same polarity as the non-image and opposite polarity to thenon-image signal in one frame.
 18. The liquid crystal display device asdescribed in the claim 17, wherein a polarity of the non-image signalwhich is sequentially written after an image signal in each of thepicture-element cells in one frame period is different from the polarityof the image signal.
 19. The liquid crystal display device as describedin the claim 17, wherein a polarity of the non-image signal which issequentially written after an image signal in each of thepicture-element cells in one frame period is same as the polarity of theimage signal.